Abstract
Selective erosion of fine particles from granular soils can affect the draining properties of hydraulic structures with time, and it is important to identify unstable soils and characterise their hydraulic and erosional behaviour. To this end, this study focuses on the design and set-up of a new laboratory device for testing the suffusion and piping phenomenon occurring in an internally unstable cohesionless material. The proposed procedure offers the possibility of quantifying the hydraulic gradient at which erosion starts and evaluates the mass of fine particles washed out of the sample under controlled hydraulic conditions. The quantity of eroded particles, the exit water flow rate and the hydraulic gradient distribution along the flow paths are also measured during the process. The procedure was tested on an erosive soil under saturated conditions and under unconfined seepage, allowing the assessment of the hydraulic behaviour of this internally unstable material.
Highlights
Practical rules derived from theoretical and experimental studies define filter criteria to prevent water-related damages on granular media (Burenkova, 1993; Cedergren, 1985, 1988; Kenney and Lau, 1985, 1986; Lafleur, 2003; Lafleur and Savard 2004; Sherard et al, 1984; Terzaghi, 1943)
Erosion tests are conducted to define geometrical limits between internally stable and unstable materials many authors have analysed the impact of parameters such as flow direction, stepping time intervals, hydraulic head increasing rate, volume of specimen, initial dry density and confining pressure on internal erosion (Chang and Zhang, 2011; Li, 2008; Marot et al, 2010; Moffat and Fannin, 2006; Reddi et al, 2000; Shwiyhat and Xiao, 2010; Skempton and Brogan, 1994; Wan and Fell, 2004a)
The key point of this study is to suggest an economical and easy-to-implement experimental procedure that can replicate the erosional behaviour of an internally unstable material under real in situ conditions
Summary
Practical rules derived from theoretical and experimental studies define filter criteria to prevent water-related damages on granular media (Burenkova, 1993; Cedergren, 1985, 1988; Kenney and Lau, 1985, 1986; Lafleur, 2003; Lafleur and Savard 2004; Sherard et al, 1984; Terzaghi, 1943). Even if a material is well selected, segregation may occur under field conditions due to placement or compaction or even during cyclic loading (Chapuis et al, 1996) In such cases, selective erosion of fine particles from a matrix of coarse soil particles could exhaust the drainage system of earthen hydraulic structures with time (Lafleur and Savard, 2004). Shwiyhat and Xiao (2010) investigated changes in the permeability and volume of soils during the internal erosion process under a constant hydraulic gradient using a triaxial cell These experimentations pointed out that settlements and permeability reduction might occur in soil specimens after suffusion
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